1. Field of the Invention
The present invention relates to apparatus and method of forming a spacer for use in a liquid crystal panel, wherein the spacer is disposed between two substrates that together form the liquid crystal panel and thereby secures a spacing between the substrates.
2. Description of the Related Art
FIG. 13 is a view showing a structure of a liquid crystal panel employed in a display device of a computer or the like.
The liquid crystal panel 201 is formed by placing a lower substrate 203 and an upper substrate 205 to oppose each other, and sealing a liquid crystal material 207 in a space between the substrates 203 and 205.
The lower substrate 203 has a glass substrate 203a, on one surface of which is formed a circuit layer 203b including pixel electrodes, thin film transistors (TFTs), MIM forming elements, matrix wiring, etc., and on the other surface of which is formed a phase difference plate 203c, with the circuit layer 203b being faced toward the upper substrate 205.
The upper substrate 205 has a glass substrate 205a, on one surface of which are formed electrodes, a color filter 205b, etc., and on the other surface of which is formed a phase difference plate 205c, with the color filter 205b being faced toward the lower substrate 203.
The substrates 203 and 205 are placed to oppose each other with spacers 209 being sandwiched in between, and thereby secure a spacing between the substrates 203 and 205, into which the liquid crystal material 207 is sealed.
The liquid crystal material 207 is sealed in a space between the substrates 203 and 205 as the periphery thereof is hermetically sealed with a seal 211.
A polarizing plate 213 is further deposited on the main surface side of the upper substrate 205.
Also, a polarizing plate 215, an optical film 217 used to improve a light utilization factor, an optical film 219 functioning as a prism or a lens, and a diffusing plate 221 are sequentially deposited on the back surface side of the lower substrate 203, and an optical waveguide 223 and a reflecting plate 225 are further deposited on the outside.
In addition, a lamp 227 is placed in close proximity to the optical waveguide 223 so that light is projected onto the optical waveguide 223.
Incidentally, while the display performance, such as resolution, is being upgraded, a cost reduction of the liquid crystal panel has been pursued by reducing the number of components used, improving the manufacturing method, etc.
For example, in the case of the conventional liquid crystal panel 201, transparent, cylindrical or granular beads are used as the spacers 209, and a spacing between the substrates is secured by scattering the beads across the surface of either substrate (or occasionally the both substrates) before the upper and lower substrates 205 and 203 are coupled to each other, so that the beads are sandwiched by a pair of the substrates 203 and 205.
According to this method, however, only a small number of spacers 209, which are the beads scattered over protrusions (the pixel electrodes, TFTs, MIM forming elements, matrix wiring, etc, forming the circuit layer 203b) on the lower substrate 203, are brought into contact with the upper substrate 205. This causes a load to be concentrated on the contact portions of a small number of spacers 209, which may possibly damage the elements and electrodes.
A countermeasure to avoid concentration of a load on part of the spacers 209 could have been taken by increasing a scattering density of the spacers 209. However, such a countermeasure scatters a number of spacers 209 on the display portion as well, and raises a new problem that the contrast is deteriorated.
In order to eliminate the foregoing problems, a technique, disclosed in JP-A-3-89320, has been proposed.
According to this technique, spacers are formed by applying a resin material on the surface of a lower substrate 8 composed of, as shown in FIG. 14A, a glass substrate 1 on the surface of which gate electrodes 2, an insulation film 5, drain electrodes 6, a passivation film 7, etc. are formed sequentially from bottom to top.
A more concrete procedure is as follows. That is, as shown in FIG. 14B, UV cure resin 9 is applied first across the entire surface of the lower substrate 8 in a predetermined thickness, then UV rays are irradiated to the resin 9 at portions that are not positioned above the pixel electrodes, and resin 9a on the irradiated portions is thereby cured, after which resin 9b on an uncured portion is removed. The resin 9a left in the form of pillars as shown in FIG. 14C is thus obtained as spacers.
According to this method, because the spacers are positioned on the outside of the portions above the pixel electrodes, even when the number of spacers are increased, neither the elements nor the electrodes will be damaged by a load acting on the spacers, and deterioration of the contract can be prevented. It is thus possible to obtain a liquid crystal panel with a high display performance.
This method, however, takes a long time in the coating process and the drying process for resin to be made into spacers. Also, another process is generally needed to provide a protection layer on the surface of the applied UV cure resin 9 in preventing deterioration of writing reproducibility resulted from oxygen-induced desentization during the exposure with UV rays, which raises a problem that the productivity becomes poor.
Further, in a case where spacers are formed on the substrate including a black stripe that forms a color filter, there is a possibility that the alignment layer in contact with the UV cure resin is dissolved in a solvent contained in the resin.
In order to eliminate the foregoing problems, a method of forming a spacer for use in a liquid crystal panel, disclosed in JP-A-5-11256, has been proposed.
According to this method of forming a spacer for use in a liquid crystal panel, a photosensitive sheet subjected to development processing is used. The photosensitive sheet is formed by depositing an organic polymer layer used to block oxygen during exposure and a light-cure resin layer that can be developed in a water-based developer on a sheet-like flexible supporting body.
The procedure of forming a spacer is as follows.
Firstly, the oxygen-blocking organic polymer layer and the light-cure resin layer used for development provided on the photosensitive sheet are transferred onto at least one of two substrates that together form a liquid crystal panel.
Then, the light-cure resin layer transferred onto the substrate is subjected to pattern exposure at positions that do not overlap the pixel electrodes on the substrate or at local positions corresponding to the portion above the black stripe forming the color filter. Cured portions that will be used as the spacers are thus obtained.
Subsequently, an unexposed portion on the substrate is removed through development processing, and as a consequence, only the portions of the light-cure resin layer cured through exposure are left on the substrate as the spacers.
According to this method of forming a spacer for use in a liquid crystal panel, as shown in FIG. 15 for example, in a pixel array on the surface 13 of the substrate used to form the liquid crystal panel, it is possible to form spacers 14 for the sets of pixel electrodes 11r, 11g, and 11b respectively provided with RGB color filters on a one-to-one basis exactly in a narrow region 15 between pixels 11 or at a position on the black stripe. Consequently, concentration of a load on the spacers can be reduced. Also, because exposure is performed while the surface of the substrate is covered with the oxygen-blocking organic polymer layer, oxygen-induced desentization will not occur, which makes it possible to prevent deterioration of writing reproducibility. Further, even in a case where spacers are formed on the substrate having the black stripe, a possibility that the alignment film is dissolved in a solvent contained in the resin layer is eliminated. Moreover, because neither the coating process nor the drying process that takes a long time is needed, the productivity can be improved.
According to the method of forming a spacer for use in a liquid crystal panel in the publication supra, however, after the photosensitive sheet is transferred onto the entire surface of the substrate used to form the liquid crystal panel, an unexposed portion that accounts for greater part thereof (approximately 99.82% in the case of the array of spacers shown in FIG. 15) is removed and discarded through the development processing, which raises a problem that the materials are used wastefully.
Also, there is another problem that high-cost treatment of waste liquid, such as a developer, makes it difficult to reduce the manufacturing cost of the liquid crystal panel.
Further, a highly accurate mask is needed to expose the light-cure resin layer only at the portions that will be used as the spacers, and the manufacturing cost of the mask increases with an increase of the size of the substrate. This raises still another problem that this method is not suitable to a large-scaled liquid crystal panel.
The invention has an object to provide apparatus and method of forming a spacer for use in a liquid crystal panel, capable of economizing materials used for spacers and reducing a quantity of waste of the materials used or the like while making it possible to reduce concentration of a load on the spacers, prevent deterioration of writing reproducibility, prevent dissolution of the alignment film, improve the productivity, etc.
The invention provides a method of forming a spacer for a liquid crystal panel, said spacer being disposed between two substrates that together form the liquid crystal panel to secure a spacing between said substrates, including steps of superposing a transfer sheet on a surface of one of said two substrates; recording a desired image pattern onto said transfer sheet by image recording process through the use of one of a laser beam and heat; and peeling off said transfer sheet to form said image pattern transferred onto said substrate.
In the method of forming a spacer of the invention, in a case where a color filter having a black stripe is placed on said substrate on which said image pattern is to be formed, a transfer position of said image pattern may be set on said black stripe.
In the method of forming a spacer of the invention, a maximum width of said image pattern to be transferred onto said black stripe may be set two or less times greater than a width of said black stripe.
According to the method of forming a spacer, an image recording method for transferring an image pattern recorded in a transfer sheet onto the substrate by using a laser beam or heat is applied to form a spacer. Therefore, it is possible to form a number of spacers, for example, in a narrow portion between pixels, by high-precision process at high accuracy that can be achieved by an image recording technique. Hence, because a load can be dispersed to a number of spacers, concentration of a load on the spacers can be reduced. It is thus possible to prevent damages to the elements and the circuits on the substrate caused by an excess load.
Also, the forming position of the spacers can be limited to a portion where the presence of the spacers do not adversely effect the display performance, for example, a portion between adjacent pixels on the substrate used to form the liquid crystal panel or a portion on the black stripe. It is thus possible to prevent the occurrence of inconveniences, such as deterioration of contrast and deterioration of writing reproducibility.
In the method of forming a spacer of the invention, said transfer sheet is reused until a remaining non-recorded portion, where said image pattern is not recorded, reaches a specified level or below by repetitively performing steps of superposing said transfer sheet on said substrate at a position shifted from a position exposed last, so that the non-recorded portion undergoes the image recording process next; performing the image recording process; and peeling off said transfer sheet from said substrate side.
Therefore, it is possible to prevent such an event that the transfer sheet used as a recording medium is discarded with a large quantity of an unexposed portion left thereon. Hence, the materials used for spacers can be economized and a quantity of waste of the materials used or the like can reduced, thereby making it possible to achieve environmental protection through effective utilization of resources and a reduction of waste.
In the method of forming a spacer of the invention, said image pattern is repetitively transferred onto a same point on said substrate used to form the liquid crystal panel, so that a spacer of a desired height is formed.
Therefore, a height of the spacer can be readily changed.
In the method of forming a spacer of the invention, said image pattern to be transferred is reduced gradually in size each time transferring is performed when said spacer of the desired height is formed.
Thus, a contact area between the tip end and the opposing substrate becomes so small that even when the spacer is transferred and formed at a slightly shifted position, the tip end will not go outside of the position where it is supposed to come into contact with the opposing substrate. This makes it possible to ensure a spacing between the substrates in a more secure manner.
The invention provides an apparatus for forming a spacer for use in a liquid crystal panel, said spacer being disposed between two substrates that together form the liquid crystal panel to secure a spacing between said substrates, has a stage for supporting at least one of said two substrates; a recording medium supply portion for supplying a recording medium onto said substrate placed on said stage; a recording head for forming a desired image pattern onto said recording medium placed in piles through the use of one of a laser beam and heat; recording medium peel-off means for peeling off said recording medium from said substrate; and recording medium reattachment means for returning said recording medium onto said substrate by shifting a position of said recording medium to set a non-recorded portion remaining on said recording medium peeled off by said recording medium peel-off means as a next recoding portion of said image pattern.
According to the apparatus for forming a spacer, a method of forming a spacer for use in a liquid crystal panel is achieved through image recording process, and the concrete arrangement of the apparatus is the same as that of an existing recording apparatus that forms an image, such as a color filter, on the substrate. Hence, by developing the existing recording apparatus, the manufacturing cost can be reduced by minimizing the need for extra special facility on one hand, and improving the operating rate of the existing facility on the other hand.
In the apparatus for forming a spacer of the invention, the apparatus further has temporary storing means for temporarily storing said recording medium peeled off by said recording medium peel-off means.
According to the apparatus for forming a spacer, for example, by forming the temporary storing means with a capability of accommodating plural kinds of recording media separately, the apparatus can be used to form a spacer by selectively using plural kinds of recording media.
Also, by incorporating a mechanism that shifts the positioning reference position on the recording medium when the recording medium is returned onto the substrate into the temporary storing means provided at the fixed position, positioning control in positioning a non-recorded portion of the recording medium with respect to the spacer forming portion on the substrate can be performed more readily.
Also, the apparatus of forming a spacer for use in a liquid crystal panel as described above can be readily achieved by adding temporary storing means to the recording medium supply portion in an existing recording apparatus that forms an image, such as a color filter, on the substrate used to form the liquid crystal panel, and therefore, the capital investment can be reduced.
In the apparatus for forming a spacer of the invention, said recording head switches wavelength of laser beam from which is output in associated with a recoding medium used to form a color filter and a recording medium used to form a spacer each having a different recording wavelength.
Thus, because the recording head can switch the output wavelengths, an existing recording apparatus that forms an image, such as a color filter, can be used.
In the apparatus for forming a spacer of the invention, said recording head has first recording head that outputs first laser beam in associated with a recoding medium used to form a color filter and a second recording head that outputs second laser beam in associated with a recording medium used to form a spacer, wavelengths of the first laser beam and the second laser beam are respectively different.
Thus, because two recording heads that output different wavelengths are provided, an existing recording apparatus that forms an image, such as a color filter, can be used.